We plan to study the structure and expression of the receptor IgM molecule on mouse B lymphocytes. Protein microsequencing and other microchemical techniques will be employed to characterize the differences between the membrane-bound receptor-IgM molecule and the secreted serum IgM molecule. We also will investigate the orientation and interactions of the receptor IgM molecule in the plasma membrane using cell-surface labeling reagents, crosslinking reagents and antibodies to specific portions of the IgM molecule. Finally, we will characterize the gene (or genes) encoding the micron chain and the pathway of RNA transcription and processing using recombinant DNA techniques and DNA sequencing.